Generally, image sensors are semiconductor devices that can convert optical images into electrical signals. Image sensors are roughly divided into charge coupled devices (CCDs) and complementary metal oxide semiconductor (CMOS) image sensors (CIS). CMOS image sensors may have a structure in which a photodiode region converting optical signals into electrical signals and a transistor region processing the electrical signals are horizontally disposed. In a horizontal type image sensor, since the photodiode region and the transistor region are horizontally disposed in a semiconductor substrate, there is a limitation in expanding an optical sensing part (referred to as “fill factor”) within a limited area.